1. Field of the Invention
The present invention relates to an apparatus which encodes image signals by means of image processing and particularly to an image signal encoding apparatus which appropriately controls quantization step size in accordance with frame skip numbers or generated data amounts.
2. Prior Art
In apparatuses which encode and transmit image signals, the amount of code which is generated varies greatly depending on the degree of movement of the subject images. On the other hand, as the capacity of the transmission path is predetermined, a buffer memory is used for the purpose of smoothing the fluctuating generated data. Furthermore, a method is known for appropriately controlling the quantization step size in accordance with the amount of generated data and thus controlling the degree of space resolution. For example, in Japanese Patent Application, First Publication Laid Open Number SHO 63-3586, an apparatus was disclosed which appropriately controlled a quantization threshold by means of a control circuit from the accumulation amount of a buffer memory.
In the above-described prior art, quantization step size was controlled directly according to the accumulation amount of a transmission buffer memory or according to movement vector data, and precise quantization step size control in accordance with the amount of use of the buffer or variations in transmission data amount could not be conducted, so that there was a problem in that improvement in picture quality was insufficient.